i realise that these woods are at their most colourful when first cut or sanded but can we stop them dulling with prolonged ultraviolet ?. i see finished / sprayed guitars with colourful purpleheart.... does the cellulose finish keep the colour from fading ?
purpleheart will fade no matter what, unless finished and kept in the dark. A UV-resistant finish will slow it somewhat, but if it is in the light, it will fade. I've made quite a few turned pens with purpleheart, and the ones that have been in the sun are now brown, while the ones that were hidden in a drawer are still purple.
If you want purple wood, you will probably need to dye. I have no idea how to do that.
UV-additive finish is the answer, however, I've found it commercially in only good marine spar varnish, which is too soft for instruments. I've had this paudauk neck finished for over two years now, but kept in its case, has kept the color well. If left out much at all, it would turn a medium brown. Makes nice necks, though. I have worked with purpleheart, and my opinion is that one has to be somewhat of a masochist to attempt that. Hard stuff. This was finished in nitro.
very helpful answers folks. thanks